The feminists at Jezebel have a post about why it's nonsense for men, when feminists say "men do x", to say "Not all men."

The universe holds immutable truths: matter cannot be created or destroyed, an object in motion will stay at motion unless acted on by an outside force, and any time a woman points out sexist bullshit, some hero's opinion will gallantly ride in on a fedora, chiming in "Not All Men!"

Now, thanks to the internet's collective sillybrain, Not All Men! has gone from an irritating trope to a funny, giddy skewering of point-missing folks whose knee jerk reaction as part of a privileged group is to defend themselves against implications that they, as members of the complained-about privileged group, might be complicit in the status quo. It's defensive bullshit that doesn't really do anything but prove the bearer of Not All Men is more concerned with saving face for themselves than, you know, actually acknowledging the concern that another person is expressing. In the Not All Men mind, it's worse to be called sexist than to actually be a victim of sexism. Here are some typical places to find Not All Men in the wild:

Of course, while she's describing specifically male behaviors, committed mostly by men (in some cases also by a few aggressive lesbians) her belief is that it's wrong to ask feminists not to slander all men. This is the exact opposite of what we're supposed to think about minorities and women, though. Bad drivers? Not all women! Weaker and less effective at fighting than men? Not all women!

Joan Walsh, a Nice White Lady who is “editor at large” at Salon, commented that whites had no business complaining about racial epithets (even if they preceded what in one way or another was actually a hate crime) because

“no social order has ever been devised whereby African-Americans oppress people they deride as 'crackers'.”[Crackers, please… | Who cares if Trayvon Martin called George Zimmerman a “creepy ass cracker”? White grievance-mongers, that’s who, June 27, 2013]

This, of course, is not true, any more than it's true that no social order has ever been devised whereby women oppress the men they deride as privileged sexists :

College women getting raped, like, all the time? Not all men!

Not actually happening—see The Campus Rape Myth, Heather Mac Donald, City Journal Winter 2008. The one case she mentions of a genuine rape, as a counterexample to the mythical ones is this:

Just as a reality check, consider an actual student-related rape: in 2006, Labrente Robinson and Jacoby Robinson broke into the Philadelphia home of a Temple University student and a Temple graduate, and anally, vaginally, and orally penetrated the women, including with a gun.

Once again, it's not all men. Members of non-Asian minority groups are much more likely to commit domestic violence. Nicole Brown Simpson (Mrs. O. J. Simpson) could explain that to you—if she were alive. Perhaps Derbyshire rules apply to marriage, too.

Bosses who talk over you in meetings? Not all men!

All right, I admit that bosses are mostly men, and even mostly white men, although from the point of view of the bosses, it may be "Female employees who, once you get them started, don't shut up."